In the early twentieth century more than 1000 new North American Crataegus species were described by a small number of influential botanists. The most prominent of them was Charles Sargent who described an astounding 732 new species in Crataegus while director of Harvard University’s Arnold Arboretum. The large number was the result of keen field observation combined with a narrow species concept. Understanding his delimitation of species is complicated by his idiosyncratic and often confusing way of citing type and other specimens and his unique type-specimen concept. Examples of Sargent’s citations discussed here provide evidence of the way he viewed types and the association of the name with a living “type tree.” It is unclear what contact Sargent had with the international taxonomic community that was actively attempting to standardize the nomenclatural process. Near the end of his career, however, Sargent began to designate a single specimen as a type. Sargent’s frequent failure to designate a single type specimen creates a need for lectotypification in order to properly assign names. Lectotypification of names for species in Crataegus series Coccineae has recently been resolved.

Key words: Charles Sargent, Crataegus, lectotypification, type specimen